To eliminate erosion and safety hazards in one of the system's canal, a stormwater system with ditch bottom inlets was installed. Photo: Orange County Public Works Department

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During several projects, a bypass system was built to protect construction sites from the quick-rising waters that are typical of central Florida's wet season.

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A Florida public works department used rip-rap to stabilize rivers in a canal system that suffered severe erosion in the aftermath of a destructive hurricane season.

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Drains Relieve Pressure

Nashville Avenue Pond, which had just been constructed a year earlier, underwent several areas of bank failure after the hurricanes.

Rapid draw-down of pond water had caused the build-up of hydrostatic water table pressure within the pond banks, which in turn caused slope failure, according to a geotechnical analysis. The county determined that underdrains in the pond banks would relieve hydrostatic pressure.

In addition, the county found that the pond slopes were constructed steeper than the original design and were full of unsuitable fill that needed to be replaced with clean sand fill before the banks could be graded to a less steep slope. That would provide a stable pond bank slope without the need for artificial armoring.

Erosion and sedimentation in the pond were a significant water quality concern because two drain wells serve the pond. Those wells discharge stormwater directly into the underlying groundwater aquifer.

Since the project was a reconstruction of a previously permitted stormwater facility, no additional permitting was necessary.

Steep side slopes caused erosion problems and washouts at Lake Underhill Canal, and the washouts encroached the travelway, causing a significant amount of sedimentation.

The county determined that cable concrete was the best option in this case, and an emergency bypass system had to be specified to accommodate wet-weather flows during the rainy season.

Nashville Avenue Pond

Construction: $265,000

Design: $32,000

Lake Underhill Canal

Construction (in-house): $166,833

The Partnership Pays Off

Several possible solutions for stabilizing the stream banks were explored, and the rapid turnaround time that resulted from the partnership with NRCS and the water management districts allowed Orange County to address each portion of the project uniquely based on site conditions, flow characteristics, and access.

The project was nearly completed within the 180-day window; a couple amendments to the project were allowed to extend the time due to inclement weather.

It presented many unique situations and challenges, which the county—in partnership with the NRCS—tackled to restore those areas at least to their original state.

The various approaches used for canal stabilization illustrates the constraints and challenges experienced in the selection of materials, construction methods, and limitation of access while maintaining the existing condition of water quality by adhering to strict erosion control measures.

— Budhu is manager and White is Engineer II of the Roads and Drainage Division of the Orange County Public Works Department, Fla.